Hypervalent hydridosilicate in the Na-Si-H system.

Hydrogenation reactions at gigapascal pressures can yield hydrogen-rich materials with properties relating to superconductivity, ion conductivity, and hydrogen storage. Here, we investigated the ternary Na-Si-H system by computational structure prediction and synchrotron diffraction studies of reaction mixtures NaH-Si-H at 5-10 GPa. Structure prediction indicated the existence of various hypervalent hydridosilicate phases with compositions NaSiH (m = 1-3) at comparatively low pressures, 0-20 GPa.

Chemical Reactions and Phase Stabilities in the Si-Te System at High Pressures and High Temperatures.

Chemical reactions and phase stabilities in the Si-Te system at high pressures were explored using angle-dispersive synchrotron powder diffraction in a large-volume multianvil press together with density functional theory-based calculations. Cubic and rhombohedrally distorted clathrates, with the general formula Te@(SiTe) and wide compositional range, preceded by a hexagonal phase with the composition SiTe, are formed for different mixtures of Si and Te as starting materials. SiTe, with the structural formula Te(TeSi)(TeSi), is the very first chalcogenide with the MnSi-type structure.

Complete agreement of the post-spinel transition with the 660-km seismic discontinuity.

The 660-km seismic discontinuity, which is a significant structure in the Earth's mantle, is generally interpreted as the post-spinel transition, as indicated by the decomposition of ringwoodite to bridgmanite + ferropericlase. All precise high-pressure and high-temperature experiments nevertheless report 0.5-2 GPa lower transition pressures than those expected at the discontinuity depth (i.

Generation of pressures over 40 GPa using Kawai-type multi-anvil press with tungsten carbide anvils.

We have generated over 40 GPa pressures, namely, 43 and 44 GPa, at ambient temperature and 2000 K, respectively, using Kawai-type multi-anvil presses (KMAP) with tungsten carbide anvils for the first time. These high-pressure generations were achieved by combining the following pressure-generation techniques: (1) precisely aligned guide block systems, (2) high hardness of tungsten carbide, (3) tapering of second-stage anvil faces, (4) materials with high bulk modulus in a high-pressure cell, and (5) high heating efficiency.